Sarah Blaffer Hrdy, a Professor Emerita of Anthropology at the University of California-Davis, has just published a wonderful essay in evolutionary psychology, entitled Mothers and Others, the Evolutionary Origins of Mutual Understanding. Her basic question is: what accounts for the unique human capacity to read other minds? Her basic answer is that humans are cooperative breeders, which means both that human infants have evolved a unique ability to engage grown ups into caring for them and also that human adults are wired in for extensive shared care and the provisioning of offspring by so-called “alloparents” (i.e. non-biological parents). The interplay between infants’ commitment to enlist caretakers and adults’ willingness to serve as caretakers is the evolutionary basis of the human ability for mindreading. The book is an impressive and sustained argument for why, unlike other apes, humans are cooperative breeders, based on evidence from genetics, endocrinology, the paleontology of fossil record, primatology, comparative and developmental psychology, anthropological research among extant hunter-gatherer societies, history and even sociology. In the process, she debunks a number of assumptions prevalent in either anthropology (e.g. the prevalence of patrilocal residence patterns and the organizing role of patrilineal inheritance in human gathering-and-hunting societies) or in evolutionary theorizing (e.g. the Hunting pact or Sex contract).

While human infants uniquely compete among one another for being cared for, human adults are uniquely wired for sharing both food and the care of offspring. Not only is food sharing virtually inexistent among Great Apes (chimpanzees, bonobos, orangutans and gorillas), but also the exclusive reliance on maternal care among other apes is non-negotiable: separation from its mother almost inevitably leads to the infant’s death. Trust in others’ benevolence is a unique feature of human cognition: a human mother would never engage in cooperative breeding and shared care of her offspring unless she trusted members of her group. As Hrdy emphasizes, young mothers’ inexperience and incompetence are important causes of infants’ deaths among primates. Hence, there is competition among potential young caretakers for holding newborns. Cooperative breeding helps explain the following puzzle: on the one hand, human infants are more helpless, take longer to mature, are larger and more costly to feed, than infants of other apes. On the other hand, human hunter-gatherer mothers reproduce almost twice as fast (every 3 to 4 years on average) as other apes (every 6 to 8 years on average) (p. 102). Shared care and provisioning of offspring critically helps support the high rate of human reproduction compared to that of other apes. In hunter-gatherer societies, shared care enables the mother both to gather food for herself and her progeny and to benefit from food gathered by members of her group.

In chapter 3, Hrdy’s shared care hypothesis leads her to a friendly critical assessment of the emphasis by classical attachment theorists on the mother’s continuous and exclusive care of, and contact with, her offspring.

Although Great Apes are not cooperative breeders, cooperative breeding has been exploited by a wide variety of other species, including insects, birds and non-human primates, in particular a species of small New World monkeys called marmosets. (Whereas humans and Great Apes shared a last common ancestor some 6-7 million years ago, humans and marmosets shared a common ancestor some 30 million years ago.) Among marmoset males, there is intense competition for carrying infants around, and both male and female marmoset helpers respond eagerly to the noisy competition of begging babies by providing them with food. (As Hrdy puts it, she knows “of no other mammals whose babies are routinely more attached to their fathers than to their mothers […] Human mothers can only fantasize about such an unlikely state of affairs”, p. 88) Prolactin is a hormone known for stimulating lactation in female mammals and also to promote nurturing responses in birds and mammals of both sexes. As in marmoset fathers, the level of prolactin has been found to increase in human fathers after the birth of a newborn (p. 98).

Among infant-sharing primates where allomaternal care of infants is beneficial to mothers and where infants compete with other infants for care, neonatal coats have evolved to be distinctive (e.g. snow white): they attract the attention of potential care-givers at the risk of also attracting the attention of predators. Like infants of many species, human infants are particular endearing to human adults. In the terminology of chapter 7, human babies are “sensory traps” uniquely adapted for attracting the attention of potential caretakers, whose brains are wired to register signals from infants’ needs. In chapter 6, Hrdy reviews the evidence for the so-called “misplaced-parental-care” hypothesis, according to which members of a species “that bears helpless and slow-maturing (altricial) young and a deep history of parental care requiring parents to be sensitive to cues from needy immature creatures” are predisposed to engage in alloparental care, including the offspring of other species who dupe them (e.g. the infamous cuckoo). Hence, Hrdy reviews the evidence showing that misdirected parental care paved the way for cooperative breeding in a variety of species — including fish, eusocial insects and birds. For example, cooperative breeding developed in eusocial insects that have sterile castes of workers dedicated to supporting the offspring of the reproductive queen. Hrdy raises the question: are postmenopausal females equivalent of sterile castes of workers? She also reviews historical evidence in human history showing the extent of coerced human wet-nursing whereby subordinate women are led by economically advantaged and more powerful women to suckle others’ infants and thereby to suppress their own ovulation and reproduction (p. 206).

In chapter 8, Hrdy picks up the question: if allomaternal assistance is so beneficial for maternal fitness, why don’t all mother apes solicit help? The reason they don’t is that mother apes worry a lot about infanticide because (i) baby chimpanzees are a delectable source of proteins; (ii) elimination of a nursing infant provides a male with the opportunity for inseminating a fertile female; (iii) since female apes typically leave their natal kin to breed in other communities, they also worry about unrelated and potentially infanticide females as well. Among apes, the threat of infanticide looms so large that in subordinate females, it may be adaptive to forgo conceiving. Much of Hrdy’s account of cooperative breeding and alloparentality in humans involves the distinctive role of postmenopausal females in general and maternal grandmothers in particular. In many species of apes, postmenopausal females display peculiar altruistic behaviors: for example, Hrdy tells the story of a heroic langur monkey postmenopausal female in Rajasthan who risked her own life to protect an infant from the attack of an intruding male (pp. 251-52). But postmenopausal human females live longer (after they have ceased to menstruate) than postmenopausal females of other apes. (As a rule, the costs imposed by reproduction are such that females who breed tend to die sooner than those who do not. However, among cooperative breeders, the rule is often reversed. For example, the lifespan of a honeybee queen is measured in years, that of a worker in weeks.) As Hrdy argues, in human hunter-gatherer societies, maternal grandmothers work particularly hard at gathering food: ten years of a maternal grandmother’s postmenopausal life could help ensure that two grandchildren survived to reproductive age.

The evidence adduced by Hrdy in favor of the crucial role of maternal grandmothers in cooperative breeding, shared care and provisioning of offspring in humans leads her to a critical discussion of traditional assumptions in anthropology about the prevalence of primitive patrilocal residence patterns and the organizing role of patrilineal inheritance in human gathering-and-hunting societies. In fact, Hrdy does not merely argue in favor of the role of matrilineal kin in human cooperative breeding. Instead, what she emphasizes throughout her book is what she calls the “strategic flexibility” of the human family: “flexibility was, and continues to be, the hallmark of the human family” (p. 164). Her argument for strategic flexibility in human cooperative breeding leads Hrdy to a wonderful debunking of the notorious Hunting or Sex contract hypothesis that posited a pact between a male hunter who provided for his mate and a mate who repaid him with sexual fidelity (p. 147). As Hrdy points out, this model vastly overestimates the contribution of hunting over gathering in providing food among contemporary hunter-gatherer societies. What if the male dies, defects or diverts food to additional women? Given the importance of strategic flexibility in human parenting, a variety of alloparental care will be provided by “cads”, siblings, grandparents and cousins. Under the heading of strategic flexibility, Hrdy discusses not only the range of alloparentality in humans, but also the selectivity of maternal responses to newborns as a function of both the defects of offspring and the mother’s economic resources.

In her wonderful book, Hrdy reviews a wide range of evidence showing that cooperative breeding was discovered by many different species with widely different brain structures. In fact, Hrdy offers some fascinating speculations about the problems whose solution might have facilitated the emergence of cooperative breeding. On the one hand, “it allowed wolves, elephants, and lions (all of which were once much more widely spread around the world than they are today), along with various species like corvids, mice, and humans […] to move out of Africa, or, as in the case of many cooperatively breeding birds, Australia, migrating to almost every continent of the world” (p. 179). On the other hand, three of the enhancing conditions of cooperative breeding are: slow maturation and long lifespan; year-around occupation of the same geographical area; and unpredictable environmental changes (pp. 197-98).

In the last chapter, Hrdy considers the pair of related questions: when did human cooperative breeding first begin? When did humans become emotionally modern? By an emotionally modern human, Hrdy means a human being able to board a transatlantic flight full of strangers and to emerge on the other side of the Atlantic unscathed — something, she claims, a chimpanzee would be emotionally incapable of. As she puts it in chapter 1, if a bunch of humans were “traveling with a planeload of chimpanzees, any one of us would be lucky to disembark with all ten fingers and toes still attached […] Even among famously peaceful bonobos […] veterinarians sometimes have to be called in following altercations to stitch back on a scrotum or penis.” True, the archeological record of the past 10.000 years of modern human history abounds with evidence of human massacres. However, on Hrdy’s view, unlike members of later hierarchical human societies based on food production and the division of labor, Pleistocene pre-Neolithic ancestors of emotionally modern humans were hunter-gatherers living in egalitarian groups of low population density with little or no pressure towards warfare. She speculates that the evolutionary pressure for cooperative breeding and emotional modernity in apes came mostly from bigger brains and bigger body size (that require more food, particularly proteins), extended lifespan and prolonged childhood. On this basis, she argues that cooperative breeding and emotional modernity emerged early in hominid evolution long before language, and even before the common ancestors of all modern humans migrated out of Africa sometime within the past 200.000 years.

I share Pierre\'s enthusiasm for Hrdy\'s book. It is wide, it is deep, and it is a great read. I agree that it throws light on the evolution of mindreading. The argument that alloparenting created selective pressure for early and fine-tuned awareness of the emotions and benevolent or malevolent dispositions of others is quite strong. This is different however from the fully-fledged version of mindreading that involves the metarepresentational attribution of mental [i]contents[/i] to others. There the Machiavellian story seems more compelling. Of course, the two stories are compatible and may be complementary.

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Thanks for the reply Thom, I guess I'd assumed that the attractors you were discussing weren't the kind of computational principles I had in mind, but I'm probably wrong about that! You say that the challenge is to identify exactly what these principles are. But I gave a few in my comment and in general I think we have a pretty good idea about at least some of these principles (principles of constituency formation, of interpretive domain, of structure alteration etc). These principles may not be language specific, in that they may be used elsewhere in cognition (e.g. music, arithmetic, whatever), but it's pretty hard to explain various phenomena of human language without them and our best understanding of them comes from investigation of syntax/semantics across languages. So I guess the question for you would be, is something like Merge, or say cyclic interpretation of structure, a possible attractor in your view?

Hi Liz. Thanks for the detailed response, and apologies for the delay in replying.

You write, correctly, that “One can agree that ostensive-inferential abilities are essential and unique to linguistic communication, but still think that there are evolutionary pre-cursors that do not rely on these abilities that are ‘language-like’ in an interesting sense… on an empirical level, one… needs to assess which (aspects) of non-animal human communication systems are language-like”.

I entirely endorse looking at non-human communication systems for pre-cursors of full-blown ostensive-inferential communication. In SOM I set out tests that would unambiguously identify a communication system as ostensive-inferential; but I did not, it is true, discuss what potential “mid-points” might look like, and how we could identify them. I nevertheless agree, without reservation, that this is an important conversation to have. Mathieu’s and Katja’s comments are good starting points. Having said that, I would like to stress that what we should be looking for here are behaviours that may be partially ostensive (i.e. are produced with an intention to make it manifest to an audience that one has an intention to communicate). Yet there is almost no comparative work specifically focused on ostension. Yes, there is work on intentionality (shared or otherwise), and this is relevant, but there is very little on ostension, properly understood. I would be delighted to see more work of this sort. (I do know that there is some work on ostension in non-human species, but this is a small subset of research focused on more basic aspects of social cognition, and it is dwarfed by research programs focused on the codes used in non-human primate and other communication systems. This is what I mean by “very little”.)

Let me turn now to the three points that you argue I need to assume and/or argue for, in order to sustain my arguments:

“(1) Ostensive-inferential communication requires 4th order meta-representational capacities… but Moore has argued that Gricean communication may not require this degree of meta-psychology, in which case there are simpler pre-cursors to full-blown Gricean communication…”.

As you know, I argued in SOM that ostensive-inferential communication is a richly metapsychological activity. You are right that Richard, among others, has made counter-arguments. But I could not rebut those arguments in SOM because the detailed version of them was not published at the time. In fact, the detailed version is still is not. It is true that parts of the argument exist in some of Richard’s papers, but the most explicit versions are still under review at the moment. So how could I rebut them?

“(2) There are no ‘interesting’ stages of proto-Gricean communication, and there are no other relevant features of language that might make a communication system ‘language-like’…”

As I said above, I would happily welcome proposals of this sort. That is: I would welcome substantive proposals of what partially ostensive communication would look like. There is, again, very little work of this sort. You are right Dorit Bar-On’s work is one exception, but as I said in SOM, I do not find it persuasive.

It may also be relevant to point out that I don’t think that an author has an obligation to address all arguments contrary to their own view. Richard made a similar complaint to yours, and I stand by what I said in response: I explicitly stated in SOM that the agenda was not to provide a comprehensive overview, but to make a positive case for my own arguments. (Perhaps this is a disciplinary difference in expectations: I cannot help but notice that, of the various book club commentators, it is yourself and Richard – both originally trained as philosophers – who have complained that SOM does not discuss other positions in enough detail.)

“(3)… in terms of what was actually ‘in the lexicon’, there may have been at least some continuity in the early stages.”

I agree. But this is not the sort of continuity I argued against in SOM.

One last point. You write that “while trying to shift research attention to the core importance of pragmatics and social cognition in understanding language evolution is a good thing (though, following Bart de Boer’s comment, this is already a major research area in non-Chomskyian studies of language evolution)”. I can’t agree. If this is a major research area, why does “pragmatics” barely feature in the indexes of edited collections on language evolution? There are widespread acknowledgements that pragmatics is important, but this is mostly lip-service. Consider, for instance, research on the codes used in non-human primate communication. This is much bigger area than comparative pragmatics and, critically, this research rarely if ever consider whether the codes that are being studied are natural codes or conventional codes. This would not be the case if pragmatics was taken as seriously as it should be.

Let me respond directly.“Thom, and many others, underestimate the problems in deriving universal properties of language as a cognitive mechanism from externalities interacting with general (but innate) principles of learnability and communication following Simon (Kirby)'s work… I couldn't really care less whether these were language specific… but they are, I think, deep principles of certain aspects of cognition. My guess is that these principles interact with equally general principles of learnability, memory, processing, social structure etc, to give rise to the panoply of phenomena we see.”

I actually agree that learnability and communication are not the only factors at play here. (Simon might disagree; I don’t know.) Indeed, I said as much in SOM: “Clearly, numerous attractors are important for the cultural evolution of languages. I identified two above, for the purposes of exposition… but there will be many more” (p.124). (There is - mea culpa - a small mistake here: I should have written “Clearly, numerous factors of attraction are important for the cultural evolution of languages”. Still, I think my meaning was clear nevertheless.) So I totally agree that deep principles of cognition are critical. The challenge is to identify exactly what these principles are. As such, one important subsequent question is: are these principles language-specific? (You may not care what the answer to this question is, but many people do, including many generativists.)

The trick, of course, is showing it "clearly." As Dan points out, demonstrating the capacity to alter behavior as a function of different possible responses from target audiences shows the underlying psychology needed - I feel like this is the real reasoning hurdle. Rhesus monkeys have been shown to have some volitional control over their vocalizations (Hage et al. 2013), so maybe it's just a matter of time before they are documented vocalizing in ways that manipulate knowledge states of others. Perhaps another major limitation has to do with vocal and gestural control, in addition to mindreading abilities.

Greg gives good examples of deception in monkeys and corvids. They might even involve an intention to deceive. The deception however isn't done by means of signalling. What I would find much more surprising (and, hence, extremely interesting) would be clear cases where animals intentionally use signals in order to misinform.

Dan is being a better skeptic than I am. I also agree that the literature on deception in nonhumans, unfortunately, often ignores signaling issues. I don’t intend to play the game where Dan smacks down various empirical examples, but one more example comes to mind that directly addresses Dan’s requirement that “the agent intentionally engages in one course of action rather than another as a function of other agent’s possible responses.” Santos et al. (2006) show that free-ranging Rhesus monkeys, when faced with two containers of food – one that can be opened silently and one that can only be opened by ringing an attached bell – will preferentially choose the silent one when the researcher is averting her gaze, but will choose randomly when being viewed. These researchers definitely interpret the monkeys’ behavior as being strategically designed to manipulate others’ knowledge states, and they have similar work examining how eye gaze provides a cue to knowledge states. Of course, corvids are also well documented changing their caching behavior as a function of what conspecifics can and cannot see. I am sympathetic to the skeptical stance here, and when I teach this stuff, this is the challenge I pass on to my students. But my instincts tell me that the problem here is mostly methodological. Santos, L. R., Nissen, A. G., & Ferrugia, J. A. (2006). Rhesus monkeys, Macaca mulatta, know what others can and cannot hear. Animal Behaviour, 71(5), 1175-1181.

Greg writes: "I was curious about a statement made by Dan at the end of his comment: “As far as I know, there isn't even compelling evidence of an intended strategic use of signals in animal communication.” I am wondering what exactly qualifies in his view because to my mind there are innumerable examples of this in the nonhuman literature."

I am well-aware of the examples of deceptive behavior, including, less frequently, deceptive use of signals in the animal literature. I should have not just said but stressed that I had in mind "intended strategic uses," where the agent intentionally engages in one course of action rather than another as a function of other agents possible responses. To not just do this but intend to do this, you need to be able to represent - consciously or unconsciously, this isn't the issue - how what you do influences what other might do in response. There is no compelling evidence that I know of that shows that non-human animals do this in their signalling behavior.

Di Bitetti, whose intersting work on delayed food call among capuchin monkeys Greg cites, does not provide clear evidence of strategic thinking. Di Bitetti himself cautiously concludes: "finders seem to withhold the production of food-associated calls under certain conditions in a functionally deceptive way." Meaning, I take it, that intentional deception isn't established.

Thanks to all for interesting comments here. I think one important issue has to do with how we define “code.” I am using the word in a very general sense – a sense I believe is relevant to information theory. A code is any system of rules converting information into physical signals (numbers, letters, sounds, gestures, etc.) which then affords a computational process by which that information can be used to reduce uncertainty in a receiver. It is true, as Olivier points out, that the code model is separate from information theory, but I would argue that they seem to be used interchangeably by Thom, as well as by Sperber and Wilson et al. I maintain that we might want to put the code model straw man to bed, and instead focus on how information theory can help us address empirically the computational problem of ostensive communication.

Thom writes: “An inferential process starts from a set of premises and results in a set of conclusions which follow logically from, or are at least warranted by, the premises. A decoding process starts from a signal and results in the recovery of a message which is associated to the signal by an underlying code. In general, conclusions are not associated to their premises by a code, and signals do not warrant the messages they convey.”

Unless you limit the definition of coding quite severely, I would argue that deriving a conclusion from a set of premises is easily construed as a form of decoding. The question is in the details of how the premises are represented by structured signals and what sort of algorithmic processes constitute the logic of the derivation from those signals. This is essentially what I meant earlier when I mentioned that the limitation in our understanding is rooted in our lack of specific knowledge about how inferential communication actually works. So in describing a decoding process as recovering a message that is “associated” with the signal, I’m not seeing any specific conflict with the description of inference. Both are sufficiently vague to be mutually compatible when understood in an information theory framework. As I understand Olivier, he makes a similar point.

Thom then writes, “What is the “underlying code” that links sticking my tongue out with the sentiment that these people are all idiots (see SOM, p.7)? There is of course no such thing, and hence this is not decoding.” This reveals what I believe is a limitation in Thom’s definition of coding. I would argue that there is some relationship between the structural features of the expressive action and the likely inferences a target receiver will draw, and this relationship can be reasonably construed as a coding system of some sort. The details of that relationship aside (which, of course, is not currently understood, hence our problem), the physical signal systematically reduces uncertainty in perceivers regarding the contents of the message.

Finally, Thom states “But the point – the dividing line between coded communication and ostensive communication – is not whether inferential processes is involved, but whether inferential processes are sufficient to make communication possible in the first place.” I agree, but doesn’t this distinction break down if the coding scheme is evolved to exploit inferential capabilities?

Dan makes the important point that ostensive communication is about a particular kind of metarepresentation. I think there are good reasons to believe that the mechanisms generating these kinds of representations have a unique and identifiable developmental trajectory, and have some species-specific features, but there are also phylogenetically related systems we can observe in other animals as discussed by Katja in her commentary. I was curious, however, about a statement made by Dan at the end of his comment: “As far as I know, there isn't even compelling evidence of an intended strategic use of signals in animal communication.” I am wondering what exactly qualifies in his view because to my mind there are innumerable examples of this in the nonhuman literature. Perhaps it depends on one’s use of the word “strategic”? Functional deception in many animals (e.g., primate and bird species) satisfies the bill for me, including even chickens, not an animal with the most revered cognitive abilities. To take the chicken example (e.g., Marler, 1986), few, if any, would argue that when producing false food calls in the presence of strange females, roosters are trying to strategically change the mental state of the hens. Rather selection has likely shaped calling behavior by altering triggering mechanisms that increase copulation frequency, and thus reproductive fitness. But in other cases, such as the use of food calls in strategic ways by Capuchin monkeys (e.g., Di Bitetti, 2005), I believe there very solid reasons for assuming the mental states of other monkeys are part of the computational system, regardless of whether the monkeys are conscious of it or not.

To categorize a communicative act as ostensive must there be an explicit awareness of the specific strategic mental state manipulation? A similar question is also being considered in current debates on figurative language understanding (e.g., Gibbs, 2012). I would say no.

Katja needn’t have apologised for her poor internet connection. Her expertise on non-human primate communication ensures that, despite not being able to follow the discussion so far, her comments still make a unique and substantial contribution (as Dan indicates in his own response above).

Katja begins by asking for some clarification about the nature of ostensive signals, so let me try to provide some. Ostensive signals are those that express communicative (and hence informative) intentions. We can, in principle, do this with any behaviour at all, including all those that Katja suggests: gestures, facial expressions, eye gaze, touch, body posture, movement, vocalisations, and indeed anything else. So, to pick up on the example Katja raises, it is possible, in principle, for ostension to be expressed only with a tilt of the coffee cup. However, it is sometimes more appropriate to combine two behaviours in the one signal, and so eye contact is add to the tilt of the coffee cup (this could be because, say, the visual environment is noisy, or because there is a politeness norm that forbids just gesturing to waitresses in an impersonal manner). The two behaviours are produced as two parts of the same signal (which expresses both communicative and informative intentions). It is also possible, as Dan suggests, for two behaviours to serve these two functions independently (i.e. one expresses the communicative intention, the other expresses the informative intention), although I’d suggest that this is relatively rare.

How, then, to interpret the example Katja offers, of a chimpanzee combining a “penis offer” with an attention-grabbing behaviour like leaf-clipping? These two behaviours have functions that are, as Katya notes, superficially similar to the functions of informative and communicative intentions, respectively. The penis offer is the what, and the leaf-clipping is the that. However, this functional similarity does not imply a cognitively similarity. Informative intentions are intentions to change others’ representations of the world. An intention to simply change behaviour is not the same thing, and, as Katja and Dan both point out, it is quite possible that one or both of these behaviours is focused on behaviour rather than mental states. This is why one especially good way to test for an informative intention is to experimentally dissociate the behavioural outcome from the intended change in mental representations (SOM, p.87). I don’t know how one might do this in the case of the chimpanzee penis offer (?!), but until somebody does so, and shows that the behaviour is driven by an intention to change mental states, we cannot conclude that the penis offer is an expression of an informative intention. The story for leaf-clipping is similar. If this is an expression of a communicative intention, we need evidence that it is driven by intentions not simply to change behaviour, but rather to encourage others to mentally recognise that the chimpanzee has an informative intention. Again, we don’t have this sort of evidence for chimpanzees. If we were to acquire such evidence, I would happily change SOM’s conclusion that non-human primate communication is likely not ostensive. This would be true regardless of modality.

Katja concludes her comments with a complaint that SOM’s conclusion about chimpanzee mindreading are premature. As she rightly points out, absence of evidence is not the evidence of absence. I fear, however, that there has been a slight overinterpretation here. Nowhere do I claim that it has been shown that chimpanzees do not have command of the type and extent of mental metarepresentations in question. I claim only that “there is little evidence” for such a conclusion. I get the impression that, at present, Katja would agree.

Thanks so much for the very enlightening critique, Olivier! Like you, I'm left with a lot to chew on.

Some clarifications: I definitely don't think of enculturation as necessary for communication, for the reasons that you give. The point was about linguistic communication - a kind of communication that is easy, fluid, effortless, automatic, yet still remarkably reliable, employing the same conventions. In my view, there is a difference in kind between what transpires between two travellers who share no language when they communicate, and what transpires between two members of the same linguistic community. And it seems to me that this difference in kind can be captured rather easily with objective measures. E.g., brain areas engaged during communication, levels of stress, and other physiological markers of cognitive effort, etc.

Of course, Olivier is right that we are simultaneously members of many different cultural groups (though I think this is historically a relatively recent phenomenon). And it's plausible that we evolved a capacity to adapt to different groups as interactions among strangers grew. I've even read of some evidence that prehistoric groups were somewhat short lived, and members often had to assimilate to other groups after theirs disbanded. This would have selected for very efficient and reliable cultural learning. But none of this precludes the scientific study of cultures and socialization. These may be very fluid and vague concepts, but science makes use of those all the time, e.g., the species concept in biology. I think Olivier assumes a false alternative: either there are precise individuation conditions on some category, or it can't be studied scientifically. The history of science completely belies this. I would venture to say that most concepts used successfully in science have ended up being vague. Furthermore, there are terrific candidates for objective measures of culture and enculturation. Here's one: the interaction of social learning processes with critical period effects. It's true that we can learn from our social groups and models throughout our lifetimes. But there are limits to this, apparent in everything from accents, to phonology (Japanese r-l distinction), to, I would argue, basic values and sense of humor. I think it's plausible that this has to do with an interaction between social learning and critical periods (periods of brain development in childhood during which acquiring some trait is particularly easy relative to other periods). This is why it is so hard to acquire an accent after puberty. So one might define a culture or language group in terms of the set of people who have acquired some set of traits (language, accent, basic normative assumptions) during their critical periods. This doesn't mean that others can't acquire these traits, or that such people can't lose these traits; just that it's *relatively* much easier to acquire them inside critical periods than outside, and *relatively* much harder to lose them outside of critical periods than inside.

There are many other such objective measures possible. Just reaction time and error rates in response to basic communicative acts can easily define language groups, or maybe better, communities pf communicatively fluid interactants. Some such communities are accessible to adults, kids, or anyone who puts the effort in. Others are open only to people exposed to the appropriate social models at the apporpriate times (critical periods). Individuals are members simultaneously of many such groups. One can conceive of human brains as computers running different varieties of "cultural software" for interaction with different kinds of groups. I don't see how this kind of complexity makes notions like enculturation less scientifically tractable. Why does there need to be only one culture one is enculturated into? Why must there be a definite moment at which one counts as enculturated? Of course enculturation can come in degrees. That doesn't mean it's not scientifically tractable or real. And it doesn't mean that there aren't relatively extreme degrees of it that yield close to discrete categories: one either is a native French speaker or not (depending on what social models one was regularly exposed to, during a critical period). Another possible objective measure of culture can be derived from Boyd & Richerson's and Henrich's notion of "prestige bias". When they model cultural evolution, they assume that a basic mechanism of social transmission is made possible by "prestige bias": people imitate those who have the most social status. But judgments of social status are themsleves variable, and based on cultural assumptions about what counts as high vs. low status. In my experience, for example, financial success is a marker of high status and "emulatability" among some groups, and a marker of low status and "non-emulatability" among others. So one possible way of objectively measuring cultural phenomena is via judtgments of prestige. Individuals who regard the same social models as high prestige, and worthy of imitation (as measured by automatic dispositions to deference, tendency to attend to them when they speak, preference for interaction with over others, etc.) might be taken to constitute a cultural group.

Perhaps I'm thinking more of the notion of "mindshaping" I defend in my book here, than classical notions of socialization or enculturation, of which I know little. There is a large variety of mechanisms of social learning that appear distinctive of human beings, and that can produce relatively stable groups of communicative interactants among whom mutual interpretation is seamless, efficient, automatice, fluid, and extremely reliable (a "System 1" competence, if you like), and relative to which mutual interpretation among outgroup members is clunky, unreliable, difficult, slow, effortful, conscious. That's all I mean by "enculturation" and even if we haven't yet achieved a consensus definition of it, it takes more than this to convince me that it's not worth trying! If I may indulge in a bit of autobiography, I'm actually a Polish Canadian, and from childhood I've had to negotiate, on a daily basis, two (what appear to me) radically different cultures. It is very difficult for me to express in words the degree and subtlety of differences in expectations, assumptions, values, etc., that characterized my communicative acts and social interactions with Polish immigrants versus native Canadians growing up. Just the sorts of pragmatic implicatures on which Thom's book focuses: detecting irony, humor, etc., were most challenging. I admit that this may be my own idiosyncratic experience - perhaps I have some sort of mindreading deficit. But, judging from conversations with others in my shoes, and from interactions with other immigrants or children of immigrants whose initial language and culture were that of the old country, it is by no means a rare experience. The degree of stress I experienced over attaining status (as measured by number of friends, ease of interaction, success of attempts at humor, etc.) among native Canadians was considerably higher than among my fellow immigrants and children of immigrants. This was confirmed by others I talked to. These are real, objective properties of mutual intepretability that can be used to defined cultural groups, in my view.